High temperature, short-contacttime pyrolysis of chlorotrifluoromethane



United States Patent 3,377,391 HIGH TEMPERATURE, SHORT-CONTACT- TIME PYROLYSIS OF CHLOROTRIFLU- OROMETHANE John Richard Soulen, Narberth, and William Ford Schwartz, King of Prussia, Pa., assignors to Pennsalt Cemicals Corporation, Philadelphia,Pa., a corporation of Pennsylvania No Drawing. Filed Oct. 20, 1965, Ser. No. 499,084 6 Claims. (Cl. 260-653) ABSTRACT OF THE DISCLOSURE Chlorotrifluoromethane (CClFg) is pyrolyzed at a temperature within the range of about 1200 C. to about 2000 C. for a period of from 0.0002 to 0.05 second to produce, as the major products, 1,2-dichlorotetrafluoroethane, carbon tetrafluoride, and dichlorodifluoromethane.

This invention relates to the preparation of other organic fluoro and fluorochloro compounds by the pyrolysis of chlorotrifluoromethane. More particularly, this invention concerns pyrolyzing chlorotrifluoromethane (CClF to produce, as the major products, 1,2-dichlorotetrafluoroethane (CClF CClF carbon tetrafluoride (CR and dichlorodifluoromethane (CCl F By pyrolysis is meant the trasformation of a compound into another compound or other compounds through the agency of heat alone, and therefore the term includes not only the rearrangement of a compound but also the making of more complex compounds.

A. B. Trenwith and R. H. Watson, J. Chem. Soc., 1957, pp. 23682372, describe the pyrolysis of CClF at temperatures ranging from 700 to 850 C., whereby the principal products were CO and chlorine, with a smaller amount of CF CI and a trace amount of CR being produced. CClF CClF was not found in the reaction products. N. V. Thornton, A. B. Burg and H. I. Schlesinger, JACS, 55 (1933), pp. 3177-3182, decomposed CCIF in a high tension electric discharge to produce CR and smaller quantities of CCl F however, no chlorofluoroethanes were produced by this electric discharge technique.

It has now been discovered that high temperature pyrolysis of CClF i.e., in the range of about 1200 C. to about 2000 C., unexpectedly produces CClF CClF CF and CCl F in relatively high yields as principal reaction products, and as minor products, CF CF CCl F and CCl FCClF However, the period of the pyrolysis reaction embodied herein is very short and should not exceed about 0.05 second.

The product CE, is useful as a dielectric fluid and as a component of aerosol and refrigerant compositions. The product CClF CClF is a valuable refrigerant used mainly in systems having centrifugal rotary compressors. The product CCl F also is a kell known refrigerant. The minor product CF =CF is a starting material for preparing useful polymers. The minor product CCl F also is a well-known refrigerant and, moreover, CCl F and CCl F each can be pyrolyzed at high temperatures to produce additional CClF CClF as set forth in our copending applications, Ser. No. 497,535, filed Oct. 18, 1965 and Ser. No. 495,348, filed Oct. 12, 1965, respectively.

As stated above, the pyrolysis of CClF is carried out according to this invention at a temperature within the range of about 1200 C. to about 2000 C. The preferred temperature range, with regard to obtaining the highest conversion of the CClF and best yields of CClF CClF and CF, therefrom, is from about 1450 C. to about 1850 C.

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As earlier stated, in combination with the high pyrolysis temperatures employed in accordance with this invention, very short contact times of the CClF at such temperatures are sed. a swata times Oa hs orde at, b u 0.0002 to 0.05 second, preferably in the range of about 0.0006 to about 0.01 second. At contact times of the usual order of magnitude used in pyrolyses of this type, i.e., of h orde fa out 0; se o ds and hi he the process c this invention is inoperative because of considerable degradation of the reactant and reaction products. As used herein, contact time is defined, as follows:

contact time (seconds):

The short contact times indicated above for the pyrolysis of this invention correspond to very high space velocities ranging from about 500 to about 120,000 per hour which permit a high rate of feed and reduce reactor volume needed. Space velocity is defined as volumes of reactant (measured at standard temperature and pressure (STP), i.e., 0 C. and. 760 mm. Hg) per volume of heated reactor per hour. This is in sharp contrast to the much lower space velocities previously employed in the pyrolysis of CCIF on the order of about 9 per hour. For example, A. B. Trenwith and R. H. Watson, J. Chem. So c., ibid., used the extended reaction times of about to seconds for pyrolyzing CClF at 700 C, to 850 C.

The reaction pressure in the present process is not critical and may be atmospheric, subatmospheric, or superatomspheres. Superatomspheric pressure may range, e.g., up to about 10 atmospheres. However, atmospheric and subatmospheric pressure operation will generally be found most convenient. As a practical limit, pressures lower than about one mm. Hg abs. are not recommended. Preferred operating pressures will generally range from about 10 mm. Hg to atmospheric pressure.

The reaction is conveniently carried out by continuously passing a stream of the CClF feed through an elongated tube preferably having a high ratio of wall area to crosssectional area so that heat maybe rapidly and continuously transferred from the heated reactor walls to the gaseous reactant. The reactor should be constructed of a material resistant to attack by the reactant and reaction products at the high operating temperatures. Materials of this type include for example, inert graphite, boron nitride, and like inert materials. The reactor can be heated to the desired pyrolysis temperatures in any suitable manner such as by electrical induction heating or by placing the reactor in an electrically heated furnace.

The products of the pyrolysis passing from the reactor are cooled and usually will be scrubbed in caustic solution or other alkaline solution to remove acidic inorganic byproducts (e.g., chlorine and fluorine). The organic products are separated from the reaction mixture in a conventional manner by fractional distillation. The unreacted CClF can, of course, be recovered for recycling purposes.

EXAMPLES 1-5 In the experiments herein described, specific embodiments of the invention are set forth to illustrate and clarify the invention.

Gaseous CClF is passed continuously at a measured rate through a 4;" ID. x A2" OD. x 13" long, inert graphite tube reactor centered within a 2" diameter Vycor high-silica glass tube, 15" long. The reactor is inductively heated with a 3%" long load coil of 12 turns 3 4 of A copper tubing about the Vycof tube, the power scope of the invention which is defined by the appended for said coil supplied by a high frequency generator with claims.

TABLE I Pyrolvsis Conditions Percent Example Feed Pressure Contact Conversion Rate of mm. Hg, Temp, Time. of CClFa Weight percent in recovered converted product. oi CClFa. Abs. O. seconds gins/min. CClFzCClFg CF. 001m or =or C013? couscous;

0.440 31 1,450 0.0024 21.8 13.3 40.3 21.8 to. Nil 'lmcc 0. 405 35 12010 0. 0024 00. 2 14. s0. 2 1s. a 7. 5 0. 7 0. 0 0.352 as 1,705 0. 0033 77.9 18.4 49.2 25.3 2.7 1.0 0.0 0. 204 44 12700 0. 0050 s1. 3 17. 4 30.1 as. 7 4. 4 1.0 2. 4 0.147 21 12 550 0. 0041 85.0 28.4 34.0 21.2 2.3 5.0 0.3

a maximum output of 7.5 kilowatts operating at 450 kilo- We claim: cycles. The effective reaction zone in the tube is thus 3% 15 1. The method which comprises pyrolyzing chlorotriinches. The temperature of the reactor is measured with fiuor-omethane at a temperature of from about 1200 C. an optical pyrometer focused on the center of the heated to about 2000 C. wherein the pyrolysis time is from portion of the tube. Examination of the inert graphite reabout 0.0002 to about 0.05 second, a major product of actor after repeated runs therein reveals that its inner the pyrolysis being 1,2-dichlorotetrafiuoroethane. surface is unaffected by the passage of the hot gases 2. The method of claim 1 wherein the pyrolysis temtherethrough. perature is from about 1450 C. to about 1850 C.

The product mixture passes from the reactor and is 3. The method of claim 1 wherein the pyrolysis time condensed in a trap cooled with liquid nitrogen. The conis from about 0.0006 to about 0.01 second. denser is vented to a mechanical vacuum pump which 4. The method which comprises pyrolyzing chlorotrimaintains the subatmospheric reaction pressure employed fiuoromethane at a temperature of from about 1450 C. in these examples. After completion of the run, the reacto about 1850 C. wherein the pyrolysis time is from tion products are warmed to room temperature and transabout 00006 to 0.01 second, a major product of the ferred to an evacuated stainless steel cylinder. The reaction pyrolysis being 1,2-dichlorotetrafiuoroethane. products are then passed through a series of scrubbers 5. The method of pyrolyzing chlorotrifluoromethane containing aqueous solutions of sodium hydroxide to rewhich comprises passing chlorotrifluoromethane through move inorganic by-products. The organic reaction proda tube heated to a temperature of from about 1200 C. nets are analyzed using gas-liquid chromatographic and to about 2000" C., wherein the contact time is within infrared analyses techniques. the range of about 0.0002 to 0.05 second, a major prod- The data from five runs are summarized in Table 1. net of the pyrolysis being 1,2-dichlorotetrafiuo-roethane. In addition to the components listed in the Product 6. The method of pyrolyzing chlorotrifiuoromethane column of Table I, the reaction products contain unrewhich comprises passing chlorotrifluoromethane through acted CClF and varying minor amounts of CF CF and a tube heated to a temperature of from about 1450 C. CCl to about 1850 C., wherein the contact time is within the EXAMPLE 6 range of about 0.0006 to about 0.01 second, a major 40 product of the pyrolysis being 1,2-dichlorotetrafiuoro- The procedure of the preceding examples is repeated ethalm using an 80%platinum-20% rhodium alloy tube as the References Cit d pyrolysis reactor. The pyrolysis temperature is about UNITED STATES PATENTS 1500 C., the pressure is 25 mm. I-Ig and the contact time is 0.002 second (space velocity=9390 per hour). 3309366 11/1961 Hauptschem et 59% of the CClF fed is converted via the pyrolysis re- 1188356 6/1965 Hauptschein et 260653'S action. The principal reaction products are CF.;. (70 weight FOREIGN PATENTS percent), CClF CClF (6%) and CCilgFg (24% 1 357 773 3 19 4 France It is to be understood that the foregoing illustrative examples should not be construed as limitative of the DANIEL D. HORWITZ, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,377,391 April 9, 1968 John Richard Soulen et a1.

It is hereby certified that error appears in the above numbered ,patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 57, "kell" should read well Column 2 line 34 "superatmospheres" should read superatomospheric Columns 3 and 4, TABLE I, second column,

line 1 thereof, "0.449" should read 0.448 same TABLE, fourth column, lines 1, 2, 3, 4 and 5 thereof,

1,450 1,450 12610 1,610 1,705 should read 1,705 12790 1,790 12850 1,850

same TABLE I, ninth column, line 2 thereof, "18.3" should read 18.4

Signed and sealed this 2nd day of September 1969.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER,JR. Attesting Officer Commissioner of Patents 

